That's a classic critic against D&D if one stroke of knife is deadly IRL it should be in RPG.

That said, 3 players means a GM so just cut in half and you get 4 piece including one for the GM

The monk beats both other PCs unconscious and then uses the knife to cut off as much apple as they care to eat.

You tie the unlucky member to sacrifice. Maybe one with low fortitude. And use coup de grace. Probably it will die One shot with one stroke. Technically it's doable ^^